Faculty Publications
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Item Pulsed DC magnetron sputtered titanium nitride thin films for localized heating applications in MEMS devices(Elsevier B.V., 2018) M.a, M.A.; Lakshmi Ganapathi, L.G.; G N V R, V.; Udayashankar, N.K.; Mohan, S.Titanium nitride (TiN) thin films are deposited on Si/SiO2 substratesby using Pulsed DC magnetron sputtering and are characterized for their structural, mechanical and electrical properties for their application as localized heating elements in microsystem devices. The influence of substrate temperature on the properties of TiN films has been investigated. The correlation between the structural orientation with mechanical and electrical properties has been established. The films deposited at a substrate temperature of 300 °C have shown better structural, mechanical and electrical properties. This film has been chosen for the fabrication of microheater and its characterization. A maximum temperature of 250 °C is achieved by applying a power of 2.8 W to the microheater. © 2018 Elsevier B.V.Item Enhanced thermo-hydraulic performance in a V-ribbed triangular duct solar air heater: CFD and exergy analysis(Elsevier Ltd, 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Computational fluid dynamics (CFD) and exergy analysis are conducted to investigate the impact of secondary flow produced by V-ribs on the overall performance of a triangular solar air heater (SAH) duct. For a fixed relative rib pitch (Rp = 10) and relative rib height (Rh = 0.05), the effect of rib inclination (?) is studied using CFD technique for varying Reynolds number (5000 ? Re ? 20000). Based on the CFD simulation results, empirical correlations capable of predicting Nu and f with an absolute variance of 8.7%, and 4.7%, respectively, are developed. Employing these correlations, exergetic performance analysis is carried out. Maximum effectiveness parameter (?) of 2.01 is obtained for ? = 45° at Re = 7500. The exergy analysis reveals that the entropy generated is lower for the ribbed triangular duct compared to the smooth duct with maximum enhancement in exergetic efficiency (?ex) as 23% for ? = 45°. The study is extended for the rectangular duct to compare the performance with the ribbed triangular duct SAH (? = 45°). Results show that ribbed triangular duct SAH (? = 45°) is superior over various configurations of the ribbed rectangular duct SAH at higher mass flow rates. © 2020 Elsevier LtdItem Experimental Investigation on Heat Spreader Integrated Microchannel Using Graphene Oxide Nanofluid(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2020) Narendran, G.; Gnanasekaran, N.; Arumuga Perumal, D.A.Thermal design consideration is highly essential for efficient heat dissipation in advanced microprocessors which are subjected to conjugate heat transfer under high heat flux with a minimal area for cooling. Generally, these multicore processors develop a localized high density heat flux referred to as hotspot. The effective use of microchannel in order to mitigate the hotspot is found in literature; however, the flow induced hotspot still exist due to maldistribution of flow inside the microchannel. Henceforth, the present study provides an experimental insight on laminar forced convection in a parallel microchannel heat sink accompanied with 1.2 mm thin copper heat spreader with a surface area of 30 mm2 to effectively migrate the maldistribution flow induced hot spot. The present experimental study provides a profound insight about the hotspot and migration of hotspot to safe zones; as a result, not only the performance of the multi core microprocessor is highly improved but also the reliability of neighboring components is well secured. © 2019, © 2019 Taylor & Francis Group, LLC.Item Efficient design of an artificially roughened solar air heater with semi-cylindrical side walls: CFD and exergy analysis(Elsevier Ltd, 2020) Nidhul, K.; Yadav, A.; Anish, S.; Arunachala, U.C.Solar air heater (SAH) with semi-cylindrical sidewalls and W-baffles is analyzed for energy and exergy efficiency in the turbulent flow regime. Computational fluid dynamics (CFD) analysis is carried out for a fixed baffle inclination (?) and varying the relative baffle height (Rh = e/D) and relative baffle pitch (Rp = P/D) in the range 0.046–0.115 and 0.46–1.15, respectively. For Reynolds number (5000 < Re < 17,500), the numerical methodology is substantiated using experimental and theoretical correlations obtained from the literature. Smaller vortices near the sharp corners are removed by rounding the sharp edges, allowing the flow of fluid from inside and horizontal walls of the duct towards the semi-cylindrical sidewalls. This increases the overall turbulent kinetic energy. A peak augmentation of 3.24 and 4.03 times is obtained for Nusselt number (Nu) and friction factor (f), respectively, in contrast to conventional SAH. With a maximum enhancement of 127% in the effectiveness parameter relative to smooth SAH, this novel SAH design is evidently energy efficient. Based on CFD results, new correlations are developed in terms of Rh and Rp, which predicts the values with an absolute deviation of 4% and 7.4%, respectively. With lower exergy destruction, maximum enhancement in thermal and exergetic efficiency is obtained as 40.7% and 95.4%, respectively, for the proposed SAH relative to conventional SAH. Upon comparison with ribbed rectangular duct SAH configurations, the present design with semi-cylindrical side walls outperforms at all flow Re. © 2020 International Solar Energy SocietyItem Influence of Rectangular Ribs on Exergetic Performance in a Triangular Duct Solar Air Heater(American Society of Mechanical Engineers (ASME), 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Several artificial roughness (ribs) configurations have been used in flat plate solar air heaters (SAH) in recent years to improve their overall performance. In the present work, energy and exergy analyses of rectangular ribs in a triangular duct SAH for varying relative rib heights (e/D = 0.02-0.04), relative rib pitches (P/e = 5-15), and rib aspect ratios (e/w = 0.5-4) are evaluated and compared with smooth SAH. The analysis reveals that the entropy generated due to heat transfer is lower for the ribbed triangular duct compared to the smooth duct. It is also observed that the width of the rib plays a crucial role in minimizing heat losses to the environment. A maximum reduction of 43% and 62% in exergy losses to the environment and exergy losses due to heat transfer to the fluid is achieved, respectively, with a rib aspect ratio (e/w) of 4 compared to the smooth plate. It is found that in contrast to the smooth plate, ribs beneath the absorber plate effectively improves thermal and exergetic efficiency. Maximum enhancement of 36% and 17% is obtained in exergetic efficiency (?ex) and thermal efficiency (th), respectively, for e/w = 4, P/e = 10 and e/D = 0.04. Results also show the superiority of the ribbed triangular duct over the ribbed rectangular duct for an application requiring compact SAH with a higher flowrate. © 2020 by ASME.Item Computational and experimental studies on the development of an energy-efficient drier using ribbed triangular duct solar air heater(Elsevier Ltd, 2020) Nidhul, K.; Kumar, S.; Yadav, A.; Anish, S.Triangular duct cross-section is introduced for solar air heater (SAH) of an indirect type of solar dryer (ITSD). Using computational study, the thermo-hydraulic performance of triangular duct SAH with inclined ribs for varying rib inclination (30° < ? < 75°) in the turbulent flow regime (5000 < Re < 17500) is studied. With the rib configuration providing maximum thermos-hydraulic performance, a ribbed rectangular duct SAH is designed, and the performance of the same is compared to the former for similar heat input. Results show that the ribbed (? = 45°) triangular duct has 17% higher effectiveness compared to the latter and 79% when compared to smooth SAH. Ribs in triangular duct solar air heater facilitate the increase in temperature even in the core of the duct, delivering the air at 6 K additional temperature relative to a rectangular ribbed duct for same heat input and flow Re. The superiority of the ribbed triangular SAH is further confirmed by studying the drying characteristics of Okra and two variants of banana, namely Nendran and Robusta for the maximum temperature obtained at the outlet of the respective SAH. Various thin layer drying models available in the literature were analyzed, and Modified page model represented the drying behaviour with R2 = 0.99. For ITSD, ribbed triangular duct SAH exhibits a maximum of 60.3% reduction in moisture ratio with a maximum increase of 97.9% increase in average values of diffusivity coefficient confirming that it is an energy-efficient design for an ITSD. © 2020 International Solar Energy SocietyItem Thermo-hydraulic and exergetic performance of a cost-effective solar air heater: CFD and experimental study(Elsevier Ltd, 2022) Nidhul, K.; Yadav, A.K.; Anish, S.; Arunachala, U.C.An experimental and computational fluid dynamics (CFD) study is carried out to investigate the impact of secondary flow strengthening the thermo-hydraulic performance of discrete multiple inclined baffles in a flat plate solar air heater (SAH) with semi-cylindrical sidewalls. Initially, for a fixed relative baffle height (Rh = 0.1), the relative baffle pitch (Rp) for continuous baffles is varied in the range of 0.6–1 to obtain the optimum baffle pitch for 6000 p. A maximum thermo-hydraulic performance of 2.69 is obtained for the gap at the trailing apex. The proposed design has a higher collector efficiency, 55–70%, compared to the ribbed rectangular SAH design exhibiting 30–55%. With lower exergy losses, the present SAH design has higher exergetic efficiency (1.5%–2.2%)than ribbed rectangular SAH (0.9%–1.7%) for the range of Re studied. Further, at low Re, the present SAH design has a higher coefficient of performance, indicating that it is cost-effective than ribbed rectangular SAH designs. © 2021 Elsevier LtdItem Development of titanium nitride thin film microheaters using laser micromachining(Elsevier Ltd, 2022) M.a, M.A.; Lakshmi Ganapathi, K.L.; Ambresh, M.; Nukala, P.; Udayashankar, N.K.; Mohan, S.In this paper, we report the fabrication and characterization of titanium nitride (TiN) thin-film-based microheaters. TiN thin films have been optimized on Si and SiO2 substrates for their optimum electrical resistivities by controlling the process parameters, including argon:nitrogen (Ar:N2) ratio in reactive pulsed DC magnetron sputter (PDCMS) deposition technique. An optical emission spectroscope (OES) was used for monitoring the plasma characteristics at various nitrogen flow rates. The microstructural and surface properties of the TiN films have been investigated and correlated with the electrical properties. It has been observed that the amount of nitrogen flux in the TiN plasma plays an essential role in the microstructural, surface, and electrical properties of the TiN thin films. Micro-heaters have been fabricated with TiN thin films with low electrical resistivity using laser engraving techniques instead of conventional lithographic and micromachining techniques. The TiN microheater has shown excellent performance. A temperature of 406 °C has been achieved by applying an input power of 8 W. This work paves the path for developing scalable and economic TiN microheaters using laser micromachining techniques. © 2021Item Numerical Study for Enhancement of Heat Transfer Using Discrete Metal Foam with Varying Thickness and Porosity in Solar Air Heater by LTNE Method(MDPI, 2022) Diganjit, R.; Gnanasekaran, G.; Mobedi, M.A two-dimensional rectangular domain is considered with a discrete arrangement at equal distances from copper metal foam in a solar air heater (SAH). The local thermal non-equilibrium model is used for the analysis of heat transfer in a single-pass rectangular channel of SAH for different mass flow rates ranging from 0.03 to 0.05 kg/s at 850 W/m2 heat flux. Three different pores per inch (PPI) and porosities of copper metal foam with three different discrete thicknesses at equal distances are studied numerically. This paper evaluates the performance of SAH with 10 PPI 0.8769 porosity, 20 PPI 0.8567 porosity, and 30 PPI 0.92 porosity at 22 mm, 44 mm, and 88 mm thicknesses. The Nusselt number for 22 mm, 44 mm, and 88 mm thicknesses is 157.64%, 183.31%, and 218.60%, respectively, higher than the empty channel. The performance factor for 22 mm thick metal foam is 5.02% and 16.61% higher than for 44 mm and 88 mm thick metal foam, respectively. Hence, it is found that metal foam can be an excellent option for heat transfer enhancement in SAH, if it is designed properly. © 2022 by the authors.Item Analytical investigation on thermo hydraulic performance augmentation of triangular duct solar air heater integrated with wavy fins(Taylor and Francis Ltd., 2023) Renald, T.R.; P, S.; Matheswaran, M.; Gnanasekaran, G.Present work deals with performance improvement of triangular duct solar air heater by integration of wavy fin on absorber plate. An analytical model has been developed for the investigation of design parameters such as fin pitch ratio with ranges 0.05–0.2 and fin amplitude ratio with ranges 0.025–0.125. MATLAB code is generated to solve the energy balance equations by iterative procedure. The influence of design parameters on effective thermal and thermal efficiency is presented and its influences are discussed. Increasing the fin pitch ratio decreases the thermal and thermo hydraulic efficiency drastically. The positive effect of fin amplitude ratio is observed; increasing of fin amplitude ratio improves the thermal efficiency and effective efficiency up to the critical Reynolds number. The peak thermal efficiency of 85% is observed and thermo hydraulic efficiency of 80.16% is found at fin pitch ratio of 0.05 and fin amplitude ratio of 0.125. The maximum thermo hydraulic performance enhancement is 15.7% as it compared simple conventional solar triangular duct air extractors. The design plots are developed to select the performance parameters to attain required temperature rise values. © 2022 Taylor & Francis Group, LLC.